The X library, libX11, provides a simple input
method for characters beyond those represented on typical keyboards using
sequences of key strokes that are combined to enter a single character.

The compose file is searched for in the following order:

-

If the environment
variable $XCOMPOSEFILE is set, its value is used as the name of the Compose
file.

-

If the user's home directory has a file named .XCompose, it is used
as the Compose file.

-

The system provided compose file is used by mapping
the locale to a compose file from the list in /usr/share/X11/locale/compose.dir.

Compose files can use an "include" instruction. This allows local modifications
to be made to existing compose files without including all of the content
directly. For example, the system's iso8859-1 compose file can be included
with a line like this:

include "/usr/share/X11/locale/iso8859-1/Compose"

There are two substitutions that can be made in the file name of the include
instruction. %H expands to the user's home directory (the $HOME environment
variable), and %L expands to the name of the locale specific Compose file
(i.e., "/usr/share/X11/locale/<localename>/Compose").

For example, you
can include in your compose file the default Compose file by using:

include
"%L"

and then rewrite only the few rules that you need to change. New compose
rules can be added, and previous ones replaced.

Each event consists
of a specified input keysym, and optional modifier states:

[MODIFIER_LIST]
<keysym>

Each modifier consists of a specified modifier and a state:

(!MODIFIER
) | None

Modifiers may be preceded by a "~" character to indicate that the
modifier must not be present.

The result specifies a string, keysym, or
both, that the X client receives as input when the sequence of events is
input:

"STRING" | keysym | "STRING"keysym

Keysyms are specified without
the XK_ prefix.

Strings may be direct text encoded in the locale for which
the compose file is to be used, or an escaped octal or hexadecimal character
code. Octal codes are specified as "\123" and hexadecimal codes as "\0x123a".
It is not necessary to specify in the right part of a rule a locale encoded
string in addition to the keysym name. If the string is omitted, Xlib figures
it out from the keysym according to the current locale. I.e., if a rule looks
like:

<dead_grave> <A> : "\300" Agrave

the result of the composition is always
the letter with the "\300" code. But if the rule is: